Fracture evolution of microwave-treated concrete under uniaxial compression

In this paper, the thermal response and damage characteristics of concrete specimens under microwave irradiation were analyzed from macro and micro perspectives by uniaxial compression acoustic emission test and scanning electron microscope. The results showed that the microwave heating process can be divided into two stages: rapid heating stage (25∼100°C) and crack propagation stage (>100°C). The heating efficiency of microwave heating was the highest in the initial stage. For limestone aggregate concrete, the temperature rise rates in the time ranges of 0–40s and 40–80s were 2.11°C/s and 0.83°C/s respectively, decreasing by 60.7%. The higher the microwave power, the faster the temperature rise rate. For granite aggregate concrete, the heating rates under microwave powers of 3kW and 5kW were 0.90°C/s and 1.14°C/s respectively, increasing by 26.7%. Under the same heating conditions, the heating rate of concrete was positively correlated with the material’s loss factor, and basalt aggregate concrete (with the largest loss factor) exhibited the highest internal heating rate. The acoustic emission results showed that the internal damage of microwave heated concrete under uniaxial compression first appeared inside the specimen and then developed outwards. During the process of acoustic emission test, the damage formed in the aggregate concentrated region.